1. Field of the Invention
The present invention relates to a method for separating solder and oxide from dross of solder, a device for separating oxide, and a jet solder tank for soldering a printed board.
2. Description of the Related Art
As methods of soldering a printed board, there are known troweling, reflow, dipping and the like methods.
The troweling method is a method wherein a worker carries out soldering with a solder trowel and a solder wire in which a resin is put to each soldering portion. Thus, the troweling method is unsuitable for mass production. The main use of the troweling method is xe2x80x9cpost-solderingxe2x80x9d, wherein bad soldering generated by a different soldering method is modified, or wherein soldering is performed by a different method and subsequently an electronic component having a small heat-resistance is further soldered.
The reflow method is a method for applying a solder paste comprising powdery solder and pasty flux to a soldering portion of a printed board by printing or jetting, and then melting this solder paste in a heating device such as a reflow furnace, an infrared ray radiating device or a laser radiating device to carry out soldering. The reflow method is suitable for soldering a product having a small soldering portion, such as a surface mounted component, or a product having a narrow interval between leads. However, costs for producing the solder paste are high since the following labor is required: the solder is made into fine particles and the particles and the flux are uniformly kneaded.
The dipping method is a method for jetting a melted solder from a jet solder tank and then bringing the jetted solder into contact with a printed board to solder the board. This dipping method has far higher productivity than the troweling method and the reflow method since many soldering portions can be soldered at a time. Moreover, a solder for use is a rod-like solder, which is simple in processing; therefore, costs for producing it are low. Accordingly, the dipping method is suitable for soldering electric appliances that are inexpensive and are mass-produced, such as televisions or videos, and is most widely adopted at present.
Soldering of a printed board by the dipping method is performed in an automatic soldering machine. The automatic soldering machine is a machine having processing devices such as a fluxer, a preheater, a jet solder tank and a cooler. Moreover, in this machine, a pair of chains having many claws run from the fluxer to the cooler and above these devices. According to the automatic soldering machine, a printed board is soldered by holding the printed board with the claws between the pair of the running chains, applying flux thereto with the fluxer, preheating the board with the preheater, attaching solder thereto with the jet solder tank, and cooling the board with the cooler. The conventional jet solder tank used in this automatic soldering machine will be described referring to FIG. 1 (a plan view) and FIG. 2 (a cross section taken along Bxe2x80x94B line of FIG. 1).
A non-illustrated heater is arranged inside or outside a box-shaped body 1 of the jet solder tank. This heater causes a solder 2 put into the body 1 to be melted and causes the solder to be kept at a constant temperature. A primary jet nozzle 3 and a secondary jet nozzle 4 are set up inside the body 1. The primary jet nozzle 3 has a narrow jet opening, and means for making the jetted melted solder harsh is disposed inside the nozzle. The secondary jet nozzle 4 has a wide jet opening, and the melted solder jetted from this nozzle 4 becomes a mild flow. A rectifying plate 6 in which many holes 5 are bored is set up inside each of the nozzles. The rectifying plate 6 is a member for rectifying the melted solder, in a turbulent flow state, which is sent with a pump that will be described later, and making the melted solder toward the nozzle stable.
A duct 7 is connected to each of the nozzles 3 and 4. A jet pump 8 is fitted to the end of the duct 7. An inhalation opening 9 is made in the lower side of the duct 7 to which the jet pump 8 is fitted. A hole 11, through which an axis 10 of the jet pump 8 is inserted, is made in the upper side of the duct 7.
A non-illustrated pulley is fixed onto the upper end of the axis 10 of the jet pump 8. This pulley is connected, through a belt, to a pulley of a non-illustrated motor set up outside the body 1.
Incidentally, when a printed board is soldered in the automatic soldering machine, a great deal of dross is generated in the surface of the melted solder in the jet solder tank. When the dross is generated in great volume in the jet solder tank, the jet state of the melted solder jetted from the nozzle becomes unstable. As a result, the height of the jetted solder becomes large or small. Moreover, no jetting of the solder may be caused. This is because dross 12 floating in the surface of the jet solder tank is sucked in by the jet pump 8 as shown in FIG. 2 and the dross adheres to the holes 5 in the rectifying plate 6 set up in the nozzles 3 and 4 to block the holes 5. If the holes 5 in the rectifying plate 6 are blocked in this way, the amount of the melted solder passing through the rectifying plate 6 is reduced. Thus, the height of the jetted solder from the nozzle becomes low. Thereafter, the dross 12 blocking the holes 5 in the rectifying plate 6 is separated together with the flow of the melted solder. As a result, the amount of the melted solder passing through the rectifying plate 6 becomes large suddenly so that the height of the jetted solder becomes high. In other words, the height of the jetted solder moves up and down and becomes0 unstable whenever the dross 12 blocks the holes 5 in the rectifying plate 6 or flows out from the holes 5.
If the height of the jetted solder is not stable in the jet solder tank, the melted solder does not adhere to a printed board passing above the jet solder tank so that the printed board is not soldered. Alternatively, the height of the jetted solder becomes high suddenly so that the melted solder pours over the upper surface of the printed board. Thus, such inconveniences that the solder adheres to portions that do not require the solder arise.
The dross 12 adheres to the printed board, so that problems such as a short circuit and poor appearance arise. The cause that the dross 12 adheres to the printed board when the printed board is soldered is that in the case that the dross 12 flowing out from the holes 5 in the rectifying plate 6 together with the melted solder are jetted from the nozzle as described above, the dross 12 adheres to the printed board when the printed board passes over the nozzle.
When the amount of the generated dross 12 becomes large, such an economic problem that the consumption of the solder increases arises. This is because when the dross 12 increases, the jetted solder state is unstable as described above or the dross 12 adheres to the printed board so that a worker always takes out and throws away the dross 12 from the jet solder tank. As a result, the solder changed into the dross 12 is consumed in a large amount.
An object of the present invention is to provide a method for separating oxide and a solder from dross generated in a jet solder tank (hereinafter referred to as a separating method), a device for separating oxide from dross (hereinafter referred to as a separating device), and a jet solder tank making it possible to separate oxide from dross.
The method for separating oxide from dross according to the present invention is a method, wherein the dross floating on a melted solder in a non-oxidizing atmosphere at 100xc2x0 C. or higher is stirred together with the melted solder, thereby separating the solder and the oxide.
When the dross and the melted solder are stirred in the non-oxidizing atmosphere in this manner according to the present invention, the oxide included in the dross is separated by the stirring and the solder in the dross together with the dross dissolves into the stirred melted solder. If oxygen is present around the dross at this time, oxygen is again taken in the stirred melted solder so that the solder becomes dross. Thus, the amount of oxide and the dross increases. In the present invention, however, the dross is stirred in the state that no oxygen is present. Therefore, the melted solder does not take in oxygen.
In the separating method of the present invention, the non-oxidizing atmosphere must be 100xc2x0 C. or higher. If the non-oxidizing atmosphere is below 100xc2x0 C., the surface temperature of the dross drops so that the dross is not sufficiently separated from the oxide. In order to set the temperature of the non-oxidizing atmosphere at 100xc2x0 C. or higher, the non-oxidizing atmosphere may be heated with a gas heating heater or a heater is set inside the non-oxidizing atmosphere. Alternatively, it is allowable that air-tightness of a cover for forming the non-oxidizing atmosphere is made sufficient and the temperature of the non-oxidizing atmosphere is set at 100xc2x0 C. or higher by heat of the meted solder.
Examples of the non-oxidizing atmosphere used in the invention include inert gases such as nitrogen gas, carbon dioxide gas or argon gas; and active gases such as hydrogen gas and ammonia decomposed gas.
The device for separating oxide from dross of the present invention is a device wherein a container is provided with a heater, a cover is set over the container to be freely attachable or detachable, a non-oxidizing gas supplying opening is made in the cover or the container, and a stirring spatula for stirring the surface of a melted solder put into the container is set near the surface of the melted solder.
The separating device of the invention is a device wherein a melted solder is beforehand put into its body, dross is poured on the melted solder and then the resultant mixture is stirred to separate oxide and the solder. This separating device is located near a conventional automatic soldering machine, and dross generated in a jet solder tank is taken out from the jet solder tank and poured into the separating device. In other words, in the case that the separating device is located near the automatic soldering machine, oxide can easily be separated from the dross only by poring the dross into the separating device.
The jet solder tank of the present invention comprises a heater for heating a solder and a nozzle for jetting the solder melted by heating, wherein dross reservoir is covered with a cover, a non-oxidizing gas supplying opening is made in the cover, and a stirring spatula for stirring the surface of the melted solder is set up inside the cover.
The jet soldering tank of the present invention has therein a mechanism for separating oxide from the dross. Therefore, during soldering work, the oxide can be separated from the dross at any time.